The following discussion is not to be construed as an admission of the state of the common general knowledge.
Synthetic polymeric membranes are known in the field of ultrafiltration (UF) and microfiltration (MF) for a variety of water filtration applications. The properties of the membranes depend upon the physical properties of the membrane i.e. the symmetry or asymmetry, pore shape, pore size, and on the chemical nature of the polymer and material used to form the membrane.
Particularly important is the hydrophilic or hydrophobic nature of the membrane.
Hydrophobic surfaces are defined as “water hating” while hydrophilic surfaces are defined as “water loving”.
It is well recognized that the hydrophilic membranes generally suffer less adsorptive fouling than hydrophobic membranes. However, hydrophobic membranes usually offer better chemical, thermal and biological stability. In the development of water filtration membranes, there has been a long felt need to combine the low-fouling properties of hydrophilic polymers with the stability of hydrophobic polymers.
One approach to preparing porous polymeric membranes that possess the desirable properties of both hydrophilic and hydrophobic membranes has been simply to make various membranes from various blends of hydrophobic/hydrophilic polymers.
Previous processes for treating hydrophobic/hydrophilic blend membranes for increasing water permeability have been detailed, such as the treatment of poly(ethersulfone)/polyvinyl pyrrolidone membranes, polysulfone)/polyvinyl pyrrolidone membranes and polyvinylidene fluoride blend membranes with Cl2 as disclosed in U.S. Pat. No. 6,596,167, for example.
The present applicant has also previously explored the option of hydrophilising membranes by the use of other oxidative species, such as Fenton's agent, a source of hydroxyl radicals, in an attempt to increase water permeability of hydrophobic/hydrophilic membranes
However, there remains in the art the need for a simple process to treat membranes to increase the water permeability. It is important that any such treatment does not diminish the mechanical or other chemical properties of the membrane. It is also important that the treatment be as cost effective as possible. Further, given the extensive use of porous polymeric membranes in water filtration, it is highly desirable if the treatment does not introduce the use of potentially toxic or environmentally unfriendly species into a membrane environment.
It is also highly desirable from an efficiency point of view if the processes for treating membranes can be employed in other beneficial ways, for example, in the cleaning of membranes.